Automotive transmissions include, among other components, a clutch assembly. The interposition of the clutch assembly between a drive shaft and a driven shaft permits the drive shaft, connected to a motor or an engine, to be releasably coupled to the driven shaft. This coupling through the clutch assembly may cause the driven shaft to rotate at the same rate as the drive shaft; it may also enable a driven shaft to rotate at a different rotation rate from the drive shaft or to be completely decoupled from the drive shaft.
One component of the clutch assembly that enables the releasable coupling of the drive shaft to the driven shaft is a stack of friction elements often referred to as a clutch pack. Clutch packs typically comprise interleaved disks often referred to as clutch plates; some of these plates have friction material bonded to opposing faces of a steel core plate, often referred to as double-sided clutch plates, while others are bare steel clutch plates without any friction material. Clutch plates are alternately stacked such that the friction material on one plate contacts a mating steel reaction face of an adjacent steel clutch plate. As an alternative to double-sided clutch plates, another type of clutch plate, sometimes referred to as a single-sided clutch plate, has friction material bonded to a single face of a steel core plate with the opposing face of the steel core plate left bare. Similarly to double-sided clutch plates, single-sided clutch plates are stacked such that the friction material on one plate contacts a mating steel reaction face of an adjacent clutch plate.
Interleaved stacks of clutch plates can transfer torque from a drive shaft to a driven shaft via friction at the mating faces, or they can be decoupled from one of the shafts, thereby preventing the transfer of torque. Given this arrangement, a clutch assembly is limited in the amount of torque that it can transfer from the drive shaft to the driven shaft in part by the torque that the clutch pack can withstand without excessive slippage. When an upper frictional torque limit is exceeded, the clutch plates in the clutch pack can slip with respect to one another. Excessive slippage results in clutch performance degradation and premature clutch plate wear and failure.
As shown in FIGS. 5 and 6A, a traditional clutch assembly 10, in this example an OEM clutch assembly for Chrysler transmission model numbers 68RFE, 45RFE and 545RFE, may include an input (or drive) shaft 12, a clutch hub 14, a lip seal 16, o-rings 18 and 20, an input shaft retaining ring 22, a clutch piston 24, an o-ring 26, a lip seal 28, an annular clutch retainer 30, a retaining ring 34, a clutch reaction plate 36, reaction plate retaining rings 38 and 40, a clutch pack 42 (consisting of six externally-toothed single-sided clutch plates 44 and six internally-toothed singled-sided clutch plates 46), a clutch pressure plate 48, and pressure plate retaining rings 50 and 52.
With reference to FIGS. 5, 6A, and 6B, rotation and axial translation of the clutch assembly components occurs about and along central axis (A). Clutch reaction plate 36 and single-sided, externally-toothed clutch plates 44 have external teeth 66 and 54, respectively, located along their outer perimeters, which engage corresponding slots 56 in clutch retainer 30. Single-sided, internally-toothed single-sided clutch plates 46 have internal teeth 58 located along their inner diameters that engage corresponding external teeth on an outer surface of a driven shaft, e.g., an intermediate or output shaft (not shown). Single-sided, externally-toothed clutch plates 44 include a layer of friction material 60 bonded to one face with bare steel exposed on the opposite face; similarly, single-sided, internally-toothed clutch plates 46 include a layer of friction material 62 bonded to one face with bare steel exposed on the opposite face. Clutch plates 44 and 46 are then interleaved such that all of the friction material faces the same direction in order to create clutch pack 42. Clutch retainer 30 is held fixed axially to clutch hub 14 by retaining ring 34, and rotationally through spline 64. With respect to clutch retainer 30, clutch reaction plate 36 is held fixed axially by retaining rings 38 and 40, and rotationally by external teeth 66 that engage clutch retainer slots 56. With respect to clutch piston 24, clutch pressure plate 48 is held in place axially by retaining rings 50 and 52, and rotationally by external teeth 70, that engage slots 72 in clutch piston 24. Clutch piston 24 is indirectly located rotationally by tabs 74 on clutch retainer 30, by way of slots 75 in clutch pressure plate 48. In operation, input shaft 12, clutch hub 14, clutch retainer 30, clutch reaction plate 36, clutch piston 24, clutch plates 44, and clutch pressure plate 48 rotate in unison.
To engage traditional clutch assembly 10, as shown in FIG. 5, pressurized fluid passes through ports 76 and into the annular piston chamber 78. This fluid pressure causes clutch piston 24 to translate axially from right to left along axis (A) from the perspective of FIG. 5. This translation causes clutch pressure plate 48 to contact clutch pack 42. Once contact is established, the fluid pressure in chamber 78 causes clutch pressure plate 48 to compress the clutch plates in clutch pack 42. This compressive force generates the frictional force required to make the clutch plates in clutch pack 42 resist slippage, thereby allowing the input torque from input shaft 12 to be transferred through traditional clutch assembly 10 to an output shaft (not shown). When the clutch is engaged in this fashion, the entire clutch assembly rotates as a unit. As shown in FIG. 5, when a transmission including traditional clutch assembly 10 is properly assembled, the clutch assembly is installed along with other components within a housing 80 that protects the components from dirt and debris and helps to ensure proper lubrication is maintained.